FIG. 8 shows a cross-sectional view of a prior art semiconductor laser device disclosed in Applied Physics Letters Vol. 37, No. 3 (1980) pp 262 to 263.
In FIG. 8, the reference numeral 1b designates an n type GaAs substrate having a flat surface, the numeral 2c designates an n type AlGaAs lower cladding layer grown on the substrate 1b, the numeral 4 designates an active layer, the numeral 5a designates a p type AlGaAs upper cladding layer, and the numeral 6 designates an n type GaAs current blocking layer having a groove of a stripe configuration. The numeral 7 designates a p type AlGaAs layer grown so as to embed the groove of the current blocking layer 6, the numeral 8 designates a p type GaAs contact layer, the numeral 9 designates an n electrode, and the numeral 10 designates a p electrode.
The device operates as follows.
The light generated at the active layer 4 is confined in the active layer 4 by the refractive index difference between the active layer 4 and the adjacent upper and lower cladding layers 2c and 5a. Furthermore, the broadening of the light in the direction parallel to the active layer 4, that is in the transverse direction, is restricted by the light absorption and the current confinement by the current blocking layer 6, and the light is guided thereby.
In the prior art semiconductor laser device with such a construction, the broadening of the light in the transverse direction is restricted by the light absorption and the current confinement of the n type GaAs current blocking layer 6, and a single transverse mode oscillation is obtained when the width of the stripe of the active region is less than 5 .mu.m. Furthermore, when the injection current is increased, the refractive index distribution in the stripe varies slightly, and as a result there may arise fluctuation of the laser beam, and deviation of the current vs. light output characteristics caused by the straightness, kinks, and deviation of the peak of the far-field pattern.